The present application relates to the art of medical diagnostic imaging in which penetrating radiation is received by radiation sensitive detectors. The application subject matter finds particular use in computerized tomographic (CT) scanners and will be described with particular reference thereto. However, the invention may also find use in connection with other diagnostic imaging modalities, industrial quality assurance imaging, airport baggage inspection, x-ray fluoroscopy and the like.
Modern x-ray computer tomography scanners commonly employ several hundred x-ray detectors to convert x-ray energy into electrical signals. A detector is usually composed of a scintillator to convert x-ray energy into light and a photodiode to convert that light into an electrical current. The formats of photodiodes used in CT applications can range from a single element, 1-D arrays to a multi-element 2-D arrays.
The electrical signal from each active photodiode element is individually routed to an adjacent pre-amplifier channel. A wire bond connects a top surface bond pad on one end of the photodiode to an external connection. The conductive path to the electronics is completed using various design options. Pre-amplifiers are either located on the same PC board that includes the detector array or at a more distant location accessed by a cable.
The bond pads are typically located at one end of the photodiodes in sparse 1-D arrays. As the density of elements in the array increases, the bond pads are located on either end of the 1-D array. In still higher density arrays, the wire bonds in adjacent channels are made at alternate ends.
The wire bond density becomes even more acute for 2-D arrays. A conductive trace from each inner photodiode element in a 2-D array must be connected to the xe2x80x9coutside worldxe2x80x9d. This trace is usually included on the photodiode surface between rows of active photodiode elements. One trace is required per element and each trace usually terminates in a bond pad at an end of the 2-D array. Wire bonds from each trace are then made to external connections.
As the number of elements in a 2-D array gets large, two restrictions occur. The space required to provide room for the conductive paths between the detector rows increases and the density of the bond pads at either end of each 2-D array also increases. There is a physical limit, both in cost, function and reliability, as to the number and size of traces and bond pads that can be made using top surface contacts. A conductive path xe2x80x9cbottleneckxe2x80x9d occurs if there is not enough space on a surface to accommodate the number of traces from the photodiode bond pads to the detector electronics.
Another problem relates to degradation of the signals as they travel over the long bus system between the radiation detectors and the signal processing circuitry.
CT scanners operate in a sea of extraneous radio frequency electromagnetic signals, the frequencies of which vary over a wide band. Sources of extraneous signals include nearby operating electrical components, equipment, signals from other detectors, and the like. The long bus systems include long lead wires which inadvertently act as antennas in picking up extraneous electromagnetic signals and converting them into analog signals. The extraneous analog signals are superimposed on and mix with the analog signals from the detectors. The superimposed extraneous signals appear as noise and fictitious data when reconstructed into images. The resulting images are degraded by noise, ghosting, and other artifacts.
The present invention contemplates an improved method and apparatus which overcomes the above-referenced problems and others.
In one embodiment of the present invention, a computerized tomography imaging scanner includes a radiation sensitive detector array for converting received radiation into electrical signals. An image reconstruction processor receives the signals and reconstructs images based on the received radiation for video processing and display. The detector array includes a plurality of scintillation crystals arranged in an array where each scintillation crystal converts radiation into visible light. A plurality of back-contact photodiodes is also provided arranged in an array optically coupled with the scintillation array, and electrically coupled to the signal processing circuitry.
In accordance with another aspect of the present invention, each photodiode includes an electrical lead for communicating the electrical signals, and the detector array further includes a substrate connected on a first side to the photodiode array. The substrate is configured to provide a path on other than the first side for electrical communication between the electrical lead and processing circuitry.
In accordance with another aspect of the present invention, the electrical lead from the photodiode comprises a bump bond.
In accordance with another embodiment of the present invention, an imaging system includes an x-ray radiation source which selectively illuminates a plurality of radiation detector arrays. Each radiation detector array includes a plurality of photodetectors arranged in an array and a scintillation crystal overlaying the photodetector array for converting received x-ray radiation into visible light. The array further includes a plurality of paths below the photodetector array through a substrate providing electrical connectivity between the photodetectors and signal processing circuitry.
In accordance with another embodiment of the present invention, a method includes illuminating a radiation sensitive surface with x-rays and converting the received x-rays into light. An electrical signal proportional to the light is produced and communicated to processing circuitry via a path orthogonal to the radiation sensitive surface.
In accordance with another embodiment of the present invention, a radiation detector array includes a radiation sensitive surface which converts x-ray photons into photons of light. A photoelectric device in optical communication with the radiation sensitive surface generates electrical signals responsive to the photons generated. A first substrate supports the photoelectric device and is configured to provide an electrical path from contacts on a side of the photoelectric device opposite the radiation sensitive surface through the substrate.
One advantage of the present invention resides in locating the electrical conductors from the photodiode beneath the photodiode array.
Another advantage in one embodiment of the invention resides in freeing the light sensitive surface from electrical conductors.
Another advantage of the present invention resides in the ability to disperse a plurality of electrical leads or traces through a multi-level substrate.
Another advantage in one embodiment of the invention is that the present invention increases the active surface area of the photodiodes available to receive x-rays.
Another advantage is that it improves x-ray conversion efficiency.
Yet another advantage of the present invention resides in the ability to group a plurality of detector arrays together into a variety of configurations.
Still further advantages will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.